Cubic curve update

The author considers the problem of cataloging all the shapes that can be generated by a cubic equation. In response to a letter commenting on an earlier column, he corrects an error in his listing of all the combinations of factorizations that could make degenerate curves, pointing out that all type 5's are really the same shape and all type 7's are really the same shape. He provides additional considerations on the possible shapes of nondegenerate curves.<<ETX>>